If you've ever held your breath while swimming, you've technically freedived. Freediving liberates you from the constraints of an oxygen tank and other heavy equipment, letting you explore the ocean's underwater vistas armed solely with a big gulp of air, a mask and snorkel, a pair of fins and an optional wetsuit. When shopping for freediving fins, take into account your leg strength, fit and other criteria to ensure you're getting the best set of fins for your purposes.
Check the Ingredients
You can separate freediving fins into three categories based on what they're made of: carbon fiber, fiberglass and polymer -- sometimes known as plastic. Carbon fiber fins weigh the least and offer the best diving performance. However, they're also the most expensive and more prone to damage if you kick them against underwater rocks or reefs. Fiberglass fins are slightly cheaper and more durable than carbon fiber fins, but offer similar levels of performance. Polymer blades provide the lowest performance out of the three categories, but are also the cheapest and the most durable. Your best bet depends on your budget and how careful you are when swimming.
Swim with Stiffness
Stiffness refers to how flexible your freediving fins' blades feel. In general, stiffer fins are harder to kick with, but will propel you faster and farther. More flexible, softer fins are easier to use but will not push you as far in the water. It all comes down to your leg strength. If you're an athlete with strong legs, get fins with a hard stiffness. Medium stiffness is best for people with average muscle strength. Finally, soft fins are ideal for people with either small frames or poor leg strength.
Pick a Pocket
The part of the fin that holds your heel and foot is known as the pocket. While traditional fins have an open pocket, meaning your heel hangs out of the fin, freediving fins have a closed foot pocket to boost performance. For the best results, find a pair of freediving fins that have an interchangeable foot pocket. This means that the pocket detaches from the actual fin blades. With this setup, you can change your blades -- thus adjusting stiffness and other aspects that affect performance -- as your swimming strength or diving preferences change.
If you plan on only freediving in warm water, try the fins on with bare feet. The best fins should feel snug and tight and not come off your feet when you kick a foot up in the air. If you're planning on swimming in cold water, try the fins on with socks -- 3- to 5-millimeter socks are common choices -- or booties. Your fins will not fit well if you try them on in bare feet but end up diving with them while wearing socks or booties.